This invention relates to woodscrews or the like type of screws for use in fibrous material such as wood, particularly the self tapping screws. Such screws are typically provided with a smooth, continuous thread. This arrangement is satisfactory where the density of the workpiece of fibrous material is relatively low or where a pilot hole is provided. However, when the wood, fibrous board or the like fibrous material is relatively dense, or a pilot hole is not practical, a high torque may be required to drive the screw fully into the workpiece. It is not uncommon, particularly with the use of a power screwdriver, that the high torque requirement results in breakage of the screw. The splitting of the workpiece may also occur.
It would therefore be of advantage to have a screw for use with fibrous material which would provide a high pull-out and loosening resistance while avoiding or at least reducing the possibility of breakage of the fastener while it is driven into the workpiece.
UK Patent Specification 1,120,991 describes a wood screw wherein the thread on the shank is provided with grooves extending helically for substantially the full length of the threaded portion. Thus the thread is transformed into a number of radially outwardly projecting protuberances.
The drawback is in a substantially weakened overall torque strength of the screw and are thus prone to breakage particularly when used with a power screwdriver. Also, the cutouts do not provide sufficient space for debris formed by the cutting edge of the respective cutout. The cutouts at the tip hamper the guidance of the screw at the introduction into the workpiece.